Soldiers go separate ways, initially enjoying easy banter (8)
I believe the answer is:
repartee
'banter' is the definition.
(I've seen this before)
'soldiers go separate ways initially enjoying easy' is the wordplay.
'soldiers' becomes 'RE' (Royal Engineers).
'go separate ways' becomes 'part' (to part from someone is to leave them).
'initially' suggests taking the first letters.
The first letters of 'enjoying easy' is 'ee'.
're'+'part'+'ee'='REPARTEE'
(Other definitions for repartee that I've seen before include "Witty exchanges" , "Comic dialogue" , "Clever chat" , "Series of clever replies" , "Snappy answer" .)